Field of the Invention
The present invention relates to a light source apparatus and a method for controlling the light source apparatus.
Description of the Related Art
In recent years, more and more users of display apparatuses expect a higher level of image quality such as brightness stability, brightness gradation characteristics, and contrast. There have also been an increasing number of opportunities of using light emitting diodes (LEDs) as alight source for a backlight of a liquid crystal display apparatus.
In a light source apparatus such as the backlight, the emission brightness of a light source (the light source provided in the light source apparatus) may change as a result of an environmental change such as a temperature change or a temporal change.
Thus, a technique has been proposed in which light emitted by the light source is detected by a light sensor (brightness sensor) and in which the emission brightness of the light source is feedback-controlled so as to make a detected value from the light sensor constant (Japanese Patent Application Laid-open No. H11-295689). Such feedback control allows the emission brightness of the light source to be kept constant and enables a reduction in the brightness unevenness of light emitted by the light source apparatus.
Furthermore, when the liquid crystal display apparatus displays a black image, a liquid crystal panel fails to completely block light emitted by the backlight, leading to black floating.
Thus, a technique has been proposed which involves reducing the emission brightness of any of a plurality of light sources provided in the backlight that corresponds to a low-brightness area of input image data. Such control of the emission brightness is called “local dimming control”. Such local dimming control allows black floating to be suppressed to increase the contrast of a displayed image (an image displayed on a screen). Furthermore, the contrast of the display apparatus can further be improved by performing local dimming control and correcting the input image data so as to reduce a change in display brightness (brightness on the screen) resulting from a change in the emission brightness of the light source.
Examples of a method for controlling the emission brightness (the amount of light emission) of the light source include pulse-amplitude modulation control (PAM control) and pulse width modulation control (PWM control).
The PAM control is a control method of changing the value (pulse amplitude) of a driving signal (voltage or current) supplied to the light source to change the emission brightness of the light source.
The PWM control is a control method of changing the time (pulse width) for which the driving signal is supplied to the light source, that is, the lighting time of the light source. In the local dimming control and the feedback control, the emission brightness of the light source is generally controlled by performing PWM control.